The Greek cities of Ionia were where Herodotus’ war story began, too. These thriving settlements, which maintained close ties with their mother cities across the Aegean to the west, began, in the early sixth century B.C., to fall under the dominion of the rulers of the Asiatic kingdoms to the east; by the middle of the century, however, those kingdoms were themselves being swallowed up in the seemingly inexorable westward expansion of Persia, led by the charismatic empire builder Cyrus the Great. The fable-like arc of Croesus’ story, from a deceptive and short-lived happiness to a tragic fall arising from smug self-confidence, admirably serves what will turn out to be Herodotus’ overarching theme: the seemingly inevitable movement from imperial hubris to catastrophic retribution.

The fall of Croesus, in 547 B.C., marked the beginning of the absorption of the Ionian Greeks into the Persian empire. Half a century later, starting in 499, these Greeks began a succession of open rebellions against their Persian overlords; it was this “Ionian Revolt” that triggered what we now call the Persian Wars, the Asian invasions of the Greek mainland in 490 and 480. Some of the rebellious cities had appealed to Athens and Sparta for military aid, and Athens, at least, had responded. Herodotus tells us that the Great King Darius was so infuriated by this that he instructed a servant to repeat to him the injunction “Master, remember the Athenians!” three times whenever he sat down to dinner. Contemporary historians see a different, less personal motive at the root of the war that was to follow: the inevitable, centrifugal logic of imperialist expansion.

Darius’ campaign against the Greeks, in 490, and, after his death, that of his son Xerxes, in 480-479, constituted the largest military undertakings in history up to that point. Herodotus’ lavish descriptions of the statistic-boggling preparations—he numbers Xerxes’ fighting force at 2,317,610 men, a figure that includes infantry, marines, and camel-riders—are among the most memorable passages of his, or any, history. Like all great storytellers, he takes his sweet time with the details, letting the dread momentum build as he ticks off each stage of the invasion: the gathering of the armies, their slow procession across continents, the rivers drunk dry, the astonishing feats of engineering—bridging the Hellespont, cutting channels through whole peninsulas—that more than live up to his promise, in the Preface, to describe erga thōmasta, “marvellous deeds.” All this, recounted in a tone of epic grandeur that self-consciously recalls Homer, suggests why most Greek cities, confronted with the approaching hordes, readily acceded to Darius’ demand for symbolic tokens of submission—“earth and water.” (In a nice twist, the defiant Athenians, a great naval power, threw the Persian emissaries into a pit, and the Spartans, a great land force, threw them down a well—earth and water, indeed.)

And yet, for all their might, both Persian expeditions came to grief. The first, after a series of military and natural disasters, was defeated at the Battle of Marathon, where a fabulously outnumbered coalition of Athenians and Plataeans held the day, losing only a hundred and ninety-two men to the Persians’ sixty-four hundred. (The achievement was such that the Greeks, breaking with their tradition of taking their dead back to their cities, buried them on the battlefield and erected a grave mound over the spot. It can still be seen today.) Ten years later, Darius’ son Xerxes returned to Greece, having taken over the preparations for an even vaster invasion. Against all odds, the scrappy Greek coalition—this one including ultraconservative Sparta, usually loath to get involved in Panhellenic doings—managed to resist yet again.